added gpg key for apt repository

Isn't it better to just add the gpg key to the apt repository instead of forcing yes on the package install without gpg key?
Merge pull request #19 from Raboo/patch-1

added gpg key for apt repository
Add support for platform "amazon" in accordance to my agreement with treasure-data/chef-td-agent current
maintainer, repeatedly@gmail.com.  As per issue, Uneccesarly strick platform check #18,
  "We don't have a test environment for Amazon Linux and we don't guarantee td-agent works on Amazon Linux.
  If it is OK, please send a PR :)"
Done.

thanks!
Merge pull request #21 from benself/master

Add support for platform "amazon" (tested)
Add notice for Amazon Linux environment
Update README.rdoc

change wording a bit.
Merge pull request #22 from ijin/patch-1

Update README.rdoc
fix example to existing plugin version
Add integration tests using test-kitchen & serverspec
Fix pinning version

When pinning version, an action of package resource should be :install.

http://docs.opscode.com/resource_package.html#actions
> :install  Default. Use to install a package. If a version is specified,
>           use to install the specified version of a package.
> :upgrade  Use to install a package and/or to ensure that a package
>           is the latest version.
Merge pull request #25 from ijin/tests

Add integration tests
Install a specific version if pinning version enabled, otherwise install the latest version
Merge pull request #26 from abe4tawa8/fix-pinning-version

Fix pinning version to use correct package action
Use new repository
make port configurable
Merge pull request #27 from masarakki/port-configurable

make port configurable
Merge branch 'master' of https://github.com/treasure-data/chef-td-agent